Method and apparatus for multi-channel sensor interface with programmable gain, offset and bias

ABSTRACT

Enhanced multi-channel sensor interfaces with programmable signal adjustments are provided. An example sensor interface may include an input selector that selects one or more sensor signals from a plurality of sensor signals based on input selection control signal; an offset generator that generates an offset signal based on an offset control signal; and a programmable signal adjuster that adjusts at least one selected sensor signal based on the generated offset signal and a signal adjustment control signal. The sensor interface may include a control interface unit that generates the input selection control signal, the offset control signal, and the signal adjustment control signal. The sensor interface may include a comparator that compares output of the programmable signal adjuster with a reference signal, and provides based on the comparison an output configured for use in performing offset correction. The programmable signal adjuster may generate a number of selectable gains.

CLAIM OF PRIORITY

This patent application is a continuation of U.S. patent applicationSer. No. 15/187,730, filed on Jun. 20, 2016. The above identifiedapplication is hereby incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

Described are a method and apparatus for an integrated sensor interface,and particularly a sensor interface that provides programmablecalibration and signal conditioning for one or more channels of inputsignals.

BACKGROUND OF THE INVENTION

Many force and pressure sensors utilize a strain gauge or Wheatstonebridge circuit. The resistive elements in the bridge change resistancein response to changes in sensed condition, such as in pressure oracceleration, or mechanical strain, which in turn cause the electricaloutput (e.g., voltage or current) to change corresponding to a change inthe sensed condition.

Typical bridge sensors have a differential output signal (Vo+ and Vo−).Ideally, the unloaded bridge output is zero (Vo+ and Vo− are identical).However, inexact resistive values result in a difference between Vo+ andVo−. This bridge offset voltage can be substantial and vary betweensensors causing decreased system accuracy.

Different designs and approaches have been developed to improve thesensitivity of bridge sensors by calibrating them more accurately. Someapproaches include providing both offset correction and gain control ofthe sensor signals. Some designs attempt to address the wide range ofsensor data by having on board microprocessor to achieve programmablecompensation and calibration. However, as the deployment of smallportable devices such as smartphone gets ever broader and the userdemand for having more functions and features (thus more sensors) onsmall portable devices keeps increasing, the need in the art for asolution for highly integrated and versatile sensor conditioner orinterface design both in terms of footprint and functionality remains.

SUMMARY OF THE INVENTION

The present invention discloses a solution to the above discussedproblem. The present invention is directed to methods and apparatuses ofa highly integrated programmable sensor interface that providesprogrammable gain, offset and bias for multiple signal channels on onechip. Specifically, the programmable sensor interface according to thepresent invention provides digital offset correction for one or moredifferential input channels. The present invention provides per channelprogrammable offset, programmable gain, reference voltage and sensorbiasing using an on-chip voltage regulator. According to one aspect ofthe invention, multiple inputs are multiplexed and each is applied to avariable gain instrumentation amplifier, which connects to the output.The offset of a given channel is controlled by an on-chip DAC which hasmultiple digital storage registers, allowing each channel to have aunique, stored offset. Offsets and gains are programmed externally.According to another aspect of the invention, the sensors may be biasedby using a precision voltage regulator.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects and features of the present invention willbecome apparent to those ordinarily skilled in the art upon review ofthe following description of specific embodiments of the invention inconjunction with the accompanying figures, wherein:

FIG. 1 is a block diagram demonstrating an application of an embodimentof the invention.

FIG. 2 is a block diagram illustrating the components of an embodimentaccording to the invention.

FIG. 3 is a timing diagram of the START condition and STOP condition ofthe I2C interface on a sensor interface according to the invention.

FIG. 4 is a block diagram of an embodiment of a sensor interfaceaccording to another aspect of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail with reference tothe drawings, which are provided as illustrative examples of theinvention so as to enable those skilled in the art to practice theinvention. Notably, the figures and examples below are not meant tolimit the scope of the present invention to a single embodiment, butother embodiments are possible by way of interchange of some or all ofthe described or illustrated elements.

Moreover, where certain elements of the present invention can bepartially or fully implemented using known components, only thoseportions of such known components that are necessary for anunderstanding of the present invention will be described, and detaileddescriptions of other portions of such known components will be omittedso as not to obscure the invention.

Embodiments described as being implemented in software should not belimited thereto, but can include embodiments implemented in hardware, orcombinations of software and hardware, and vice-versa, as will beapparent to those skilled in the art, unless otherwise specified herein.In the present specification, an embodiment showing a singular componentshould not be considered limiting; rather, the invention is intended toencompass other embodiments including a plurality of the same component,and vice-versa, unless explicitly stated otherwise herein. Moreover,applicants do not intend for any term in the specification or claims tobe ascribed an uncommon or special meaning unless explicitly set forthas such. Further, the present invention encompasses present and futureknown equivalents to the known components referred to herein by way ofillustration.

Referring now to FIG. 1, a simplified block diagram illustrates a sensorsignal conditioner or sensor interface 100 designed to be coupled tomultiple bridge sensors 101_1, 101_2, . . . 101_16 and a microcontroller103. The expressions “sensor signal conditioner” and “sensor interface”are used interchangeably herein. The sensor interface 100 preferablytakes in multiple differential analog signals and serial control datafrom the microprocessor 103 as input, one analog output 104 and one LDOoutput (106), in order to provide versatility across many applications.Direct interfacing to microprocessor controllers is facilitated via anI2C serial digital interface. The sensor interface 100 is preferablycapable of running in low-voltage (0-5.5V) systems when it is combinedwith an external microcontroller 103 or field-programmable gate array(FPGA). In FIG. 1, the ADC 105 is shown as a distinct component thatconnects sensor interface 100 and the microcontroller 103. However, insome embodiments, ADC 105 can be integrated into sensor interface 100,or in the alternative, into the microcontroller 103.

Referring now to FIG. 2, a block diagram illustrates the components ofan embodiment of a sensor interface according to the invention. Thesensor interface 200 preferably includes a multiplexer block 201, anOffset block 203 and a programmable gain instrumentation amplifier block205. The multiplexer block receives the sensor output signals Input1+/−(207_1), Input 2+/−(207_2), . . . Input 16+/−(207_16) from thebridge sensors 101 (not shown). An I2C interface 209 controls the manyfunctions and features of the sensor interface 200.

Each bridge sensor connected to the sensor interface 200 has its owninherent offset that if not calibrated out can decrease sensitivity andoverall performance of the sensor system. The on-chip DAC 203 introducesan offset into the instrumentation amplifier (PGA) 205 to calibrate theoffset voltage generated by the sensors. In some embodiments of theinterface sensor according to the invention, an independent offset canbe set for each of the input channels 207. Only the offset voltage ofthe active channel is applied to the programmable gain instrumentationamplifier 205.

In some embodiments of the interface sensor according to the invention,the programmable gain instrumentation amplifier can offer 8 selectablegains from a predefined range (e.g., 2V/V to 760V/V) to amplify thesignal such that it falls within the input range of the ADC 105.

In some embodiments of the interface sensor according to the invention,the Sensor Interface also includes an integrated LDO 211 that canprovide a regulated voltage to power the input bridge sensors. As inFIG. 2, the integrated LDO 211 provides a selectable regulated voltagebetween 3V and 2.65V.

In some embodiments of the interface sensor according to the invention,LDO 211 has two operation modes: sleep mode and regular mode. The LDO211 can be set to turn off when the sensor interface is in Sleep Mode tosave power.

In some embodiments, the sensor interface 200 also supports currentsense mode. In this case, the LDO 211 also provides the ability tomonitor the LDO current. As depicted in FIG. 2, an internal 2:1 mux 213allows a voltage proportional to the LDO current to be present at theoutput. Once all channels have been calibrated, the LDO current can beused to indirectly monitor any voltage or resistive changes seen by theinputs.

In some embodiments, the sensor interface 200 also includes an internalreference voltage 215 that is used by the internal LDO circuitry 211 andused to set the reference voltage for the programmable gaininstrumentation amplifier 205.

In some embodiments, the sensor interface 200 also contains an I2Ccompatible serial interface 209. The external microprocessor programsthe sensor interface through the I2C serial interface 209 forconditioning multiple sensor signals. The various functions the sensorinterface performs include: input selection, gain selection, offsetcorrection, LDO Enable/select, Current Sense Mode, Sleep Mode (AnalogPower Down) and many other functions.

The following sections describe each of these functions in more detail.

I2C Bus Interface

The I2C-bus interface consists of two lines: serial data (SDA) andserial clock (SCL). The sensor interface works as a slave and supportsboth standard mode transfer rates (e.g., 100 kbps) and fast modetransfer rates (e.g., 400 kbps) as defined in the I2C-Bus specification.The I2C-bus interface follows all standard I2C protocols.

The sensor interface implements a basic I2C access cycle that consistsof: a start condition, a slave address cycle, Zero, one, or two datacycles—depending on the Sensor Interface on-chip register accessed, anda stop condition. FIG. 3 illustrates an I²C start and stop conditionsthat may be implemented according to one aspect of the invention.

During the Start Condition cycle, the external microcontroller initiatesdata transfer by generating a start condition. The start condition iswhen a high-to-low transition occurs on the SDA line while SCL is high,as shown in FIG. 3.

During the slave Address Cycle after the start condition, the first bytesent by the microcontroller is the 7-bit address and the read/writedirection bit R/W on the SDA line. If the address matches the sensorinterface's internal fixed address, the sensor interface will respondwith an acknowledgement by pulling the SDA line low for one clock cyclewhile SCL is high.

During the Data Cycle after the master detects this acknowledge, thenext byte transmitted by the master is the sub-address. This 8-bitsub-address contains the address of the register to access. The sensorinterface Register List is shown in Table 1. Depending on the registeraccessed, there will be up to two additional data bytes transmitted bythe master.

During the Stop Condition cycle, to signal the end of the data transfer,the microcontroller generates a stop condition by pulling the SDA linefrom low to high while the SCL line is high, as shown in FIG. 3.

I2C Bus Addressing

In some embodiments according to the present invention, Sensor Interface100 uses the higher 7 bits of a byte for addressing the I2C slave on thechip. As an example, the I2C may have an address 0x67 (0110 111X). Inthis case, a read or write transaction is determined by bit-0 of thebyte as indicated by “X”. If bit-0 is ‘0’, then it is a writetransaction. If bit-0 is ‘1,’ then it is a read transaction.

An I2C sub-address is sent by the I2C master (of the Sensor interface)following the slave address. The sub-address contains the SensorInterface register address being accessed. [Table 1 provides an exampleof the Register Information of a sensor interface embodiment accordingto one aspect of the invention.] After the last read or writetransaction, the I2C-bus master will set the SCL signal back to its idlestate (HIGH).

Inputs and Input Selection

In some embodiments according to the present invention, Sensor Interface100 includes 16 differential inputs and a 16:1 differential mux that iscontrolled by an I2C compatible 2 wire serial interface. If fewer than16 differential inputs are required, the unused inputs are tied to GND.If single ended inputs are required, the unused inputs are tied to 1.5V.

In some embodiments according to the present invention, Sensor Interface100 offers a very wide common mode range. For example, Sensor Interface100 can support a typical input common mode range of 0.6V to 2.4V whenrunning from a 3.3V supply. In most cases, the output voltage swing willbe the limiting factor.

In some embodiments according to the present invention, inputs areselected via a slave I2C interface (e.g., 203 of FIG. 2) using one of 16register addresses, such as 0x10 through 0x1F. When the sensor interfaceis powered-up, the default input may be selected as Channel 1. Theexample below illustrates how to select Channel 5.

In Step 1, a microcontroller (e.g., 103 of FIG. 1) through a Master I2C(off the sensor interface) interface sends a start signal to the slaveI2C interface (e.g., 203 of FIG. 2). In Step 2, the Master I2C sendsSensor Interface a write signal by setting bit 0 of the 8-bit data withthe higher 7 bit equal to the address of the Slave I2C interface, i.e.,0x67. In Step 3, Sensor Interface sends an acknowledge signal to theMaster I2C. In Step 4, the Master I2C sends the address of the controlregister corresponding to Channel 5, e.g., 0x14. Step 5, SensorInterface through the slave I2C interface sends acknowledgement back tothe Master I2C. Step 6, the Master I2C sends stop condition to completethe selection of Channel 5.

Gain Selection

In some embodiments according to the present invention, the sensorinterface is capable of providing multiple selectable fixed gains withina predefined voltage range. For example, a sensor interface according tothe present invention may offer 8 selectable fixed gains ranging from2V/V to 760V/V. When the Sensor Interface is powered-up, the gain is ata default value, e.g., 2V/V. The actual desired gain can be selected viaI2C through a Gain Select register. The example below illustrates how toselect a gain of 150V/V, assuming a register with address 0x06 is usedas the Gain Select register.

To start communication with the Sensor Interface, steps 1-3 as discussedabove with respect to input and output selection are repeated. Step 4,the microcontroller sends address of register to access Gain Selectregister 0x06. Step 5, Sensor Interface sends acknowledgement. Since theGain Select register is accessed, the Sensor Interface expects anotherbyte of data from the master to complete the command. Bits 0-2 of thedata byte can be used to select one of the eight pre-defined gains. Asan example, Table 1 illustrates how a Gain Register can be configuredfor a set of predefined gains. In this example, Bits 0-2 with a binaryvalue of 100 corresponds to a gain of 150V/V. So in Step 6, themicrocontroller sends a data byte of 0x04 which selects the Gain of150V/V. In Step 7, Sensor Interface sends the microcontroller anacknowledgment. In Step 8, the microcontroller sends stop condition toSensor Interface to complete the Gain selection.

TABLE 1 Gain Register Hex Bit 2 Bit 1 Bit 0 Gain 0x00 0 0 0 2 0x01 0 0 120 0x02 0 1 0 40 0x03 0 1 1 80 0x04 1 0 0 150 0x05 1 0 1 300 0x06 1 1 0600 0x07 1 1 1 760Offset Correction

In some embodiments according to the present invention, the SensorInterface has an offset correction DAC that can be used to providedigital calibration on each channel of the multiple channels of inputs.Only the offset voltage of the active channel is applied to the PGA.Using the Sensor Interface depicted in FIG. 2 as an example, the offsetcorrection DAC is a 10-bit DAC that provides an offset voltage to onlythe active channels of the 16 inputs.

The DAC offset of each channel is controlled by the I2C compatibleinterface (e.g., 203 of FIG. 2). One DAC offset register is used forstoring DAC offset of each channel. At any time, the master I2C can reador write to any of the DAC offset registers.

As an example, the DAC offset for each channel can be set via I2C usingthe register addresses 0x20 thru 0x2F followed by another two bytes ofdata to set the polarity and value of the offset voltage. In this sameexample, a ±560 mV offset correction range is available. The full rangeof the DAC offset is only available at a gain of 2. At higher gains, theoutput voltage range of The Sensor Interface will be exceeded if thefull range of the 10-bit DAC offset is used. The internal 10-bit DACallows 1,024 different offset voltage settings between 0 mV and 560 mV.The polarity of the offset correction is set with an additional bit. Theunit offset is determined by the following equation:

${{Unit}\mspace{14mu}{Offset}} = {\frac{{Total}\mspace{14mu}{Offset}}{{DAC}\mspace{14mu}{output}\mspace{14mu}{Levels}} = {\frac{560\mspace{14mu}{mV}}{1024} = {547\mspace{14mu}{\mu V}}}}$

Table 2 below lists the content of a few example offset values for a10-bit DAC offset register.

TABLE 2 DAC 10-bit DAC Range Sign Offset % Voltage D10 D9 D8 D7 D6 D5 D4D3 D2 D1 D0 FS Input RT1 0 1 1 1 1 1 1 1 1 1 1 50 +560 mV 0 0 0 0 0 0 00 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 −50 −560 mV 1 0 0 0 0 0 0 0 0 0 0 0 0

Specifically, if the content of the 10-Bit DAC register contains 0x00(hex), a 0 mV offset is applied to the corresponding active data inputchannel. If the content of the 10-Bit DAC register contains 0x3FF (hex),a +560 mV offset is applied to the corresponding active data inputchannel. If the content of the 10-Bit DAC register contains 0x7FF (hex),a −560 mV offset is applied to the corresponding active data inputchannel.

Each DAC output level provides an additional 547 μV of offset. For thesame example, the following equation can be used to determine what DACoutput level corresponds to a specific desired offset:

$X = \frac{{Desired}\mspace{14mu}{Offset}}{{Unit}\mspace{14mu}{Offset}}$

As an example, the following procedures illustrate how to set the DACoffset for input channel 7 to a value of 75 mV.

To start communication with The Sensor Interface, steps 1-3 as discussedabove in the Inputs and Input Selection are repeated. In Step 4, themicrocontroller (Master I2C interface) sends address of a DAC offsetregister to access. Following the same example above, the DAC offsetregister for input Channel 7 has a register address of 0x26. Therefore,the data byte sent is 0x26. In Step 5, Sensor Interface sends anacknowledgement to the microcontroller/master I2C.

Since a DAC Offset register was accessed, The Sensor Interface isexpecting another two bytes of data from the microcontroller or masterI2C interface to complete the command. As shown in Table 2 above, D0thru D9 are used to set the offset voltage and D10 is used to set thesign of the offset voltage, 0=positive and 1=negative.

To determine what DAC output level corresponds to 75 mV, use thefollowing equation:

${{DAC}\mspace{14mu}{Output}\mspace{14mu}{Level}} = {\frac{{Desired}\mspace{14mu}{Offset}}{{Unit}\mspace{14mu}{Offset}} = {\frac{75\mspace{20mu}{mV}}{547\mspace{20mu}{\mu V}} = 137}}$

So, a decimal value of 137 corresponds to 75 mV. Therefore, a hex value0x89 or a binary value 00010001001 in the DAC offset register wouldapply a +75 mV offset, a hex value 0x489 or a binary value 10010001001in the DAC offset register would apply a −75 mV offset.

In Step 6, the microcontroller/master I2C sends 1st byte of DAC offsetregister data to select and offset of +75 mV, i.e., the 2 MSBs of 10-bitDAC output level that corresponds to 137 (0x89). In Step 7, the SensorInterface sends an acknowledgment to the microcontroller/master I2C.

In Step 8, the microcontroller/master I2C sends 2^(nd) byte of DACoffset register data to select an offset of +75 mV. In Step 9, theSensor Interface sends an acknowledgment to the microcontroller/masterI2C. In Step 10, the microcontroller/master I2C sends a stop conditionto complete the selection of the desired offset for DAC correction for aspecific input channel, i.e., +75 mV for channel 7.

It should be noted that how the DAC connects to the PGA for effectingoffset as shown in FIG. 2 is one of the advantages the present inventionhas over the conventional approaches. In a traditional IA reference pinwould need to be used to adjust offset. This aspect of the inventionallows the sensor interface design to be more integrated with a lowernoise as well as a smaller footprint.

FIG. 4 depicts a block diagram of an embodiment of a sensor interfaceaccording to another aspect of the invention. Compared to the sensorinterface as depicted in FIG. 2, the sensor interface here (400) has acomparator (401) that compares the output signal for the PGA (403) to an“internal reference voltage” (405) and provides the comparison result toa logic circuitry (not shown). Although FIG. 4 does not depicts wheresuch logic circuitry is implemented, it should be apparent to a personskilled in the art that the logic circuitry can be implemented atvarious locations, such as within I2C Interface and Digital Logic (407),as a separate component outside of the I2C Interface and Digital Logic(407), as between Offset DAC (409) and PGA 403, or in any combination ofthese locations.

As described above, the offset correction in Sensor Interface 200 stillrequires the involvement of the user/external microprocessor, wherebythe offset is measured off Sensor Interface 200, the DAC setting is thencalculated off Sensor Interface 200 and the offset values are thenwritten into the DAC offset registers of Sensor Interface 200. UnlikeSensor Interface 200, Sensor Interface 400 allows the measurement of theoffset and calculation of the offset values carried out automaticallyand internally through just a command from the user/externalmicroprocessor.

Specifically, by adding Comparator 401 on the output and the logiccircuitry (not shown), the external microprocessor simply sends acommand to Sensor Interface 400 to initiate offset calibration. Then thelogic circuitry would begin counting up the DAC offset based on thecomparison result of Comparator 401 when the PGA output is lower thanthe desired reference voltage 405. Conversely, the logic circuitry wouldbegin counting down the DAC offset based on the comparison result ofComparator 401 when the PGA output is higher than the desired referencevoltage 405. It should be noted that although FIG. 4 shows that thereference voltage 405 labeled as “Internal Reference” is internallyprovided (e.g., 2V), the desired reference voltage 405 may be externallyapplied.

When the PGA output has reached the desired value, the counting up (orcounting down) is shut off and the register value then counted is storedfor the corresponding desired reference voltage. There are manydifferent implementations of the logic circuitry for purposes ofcounting up and counting down that are well known in the art and willnot be described here for brevity.

LDO Enable/Select (Power to External Bridge Sensors)

In some embodiments according to the present invention, the SensorInterface includes an on-chip low dropout regulator (LDO) that providesone or more regulated voltages that can be used to power external inputbridge sensors. For example, a sensor interface may provide two voltageoptions, e.g., 3V and 2.65V.

In one implementation, the LDO voltage can be selected via the I2Ccompatible two-wire serial interface. When The Sensor Interface ispowered-up, the default LDO voltage is 3V. When The Sensor Interface isactive (not in sleep mode), the LDO is always on. If the LDO voltage isnot used, the LDO output can be left floating. When the Sensor Interfaceis in Sleep Mode, the LDO can either stay on or shut down. For example,the LDO can be set to shut down while the Sensor Interface is in SleepMode to save power. Alternatively, the LDO can be set to stay on whilethe Sensor Interface is in Sleep Mode to improve wake-up time.

Similar to the configuration of the various Sensor Interface controlregisters discussed above, the LDO voltage and disable setting can beselected via I2C by configuring the control register designated for aLDO voltage control. As an example, assuming the control register forthe LDO voltage control has an address 0x07 and there are two voltageoptions to select from (e.g., 3V and 2.65V), the procedure to select avoltage of 2.65 v and keep the LDO enabled during Sleep Mode isdescribed below.

To start communication with The Sensor Interface, steps 1-3 as discussedabove in the Inputs and Input Selection are repeated. In Step 4,microcontroller/Master I2C sends address 0x07 to access the controlregister. In Step 5, Sensor Interface sends an acknowledgement.

After the LDO control register is accessed, the Sensor Interface isexpecting another byte of data from the microcontroller/Master I2C tocomplete the command. As an example, and following the same conventiondiscussed above, bit 0 and bit 1 of a data byte are used to select theLDO voltage and enable/disable the LDO during Sleep Mode. Bit 0 (D0)controls the LDO voltage (0: 3V; 1: 2.65V). Bit 1 (D1) is onlyapplicable in Sleep Mode. Bit 1 controls whether the LDO shuts down orstays on during sleep mode (0: Enable; 1: Disable). When the sensorinterface is active, the LDO is always on.

So in Step 6, the microcontroller/Master I2C sends code data 0x00 toselect LDO voltage of 2.65 and Enable LDO during the Sleep Mode. In Step7, the Sensor Interface sends an acknowledgement to the microcontroller.The microcontroller then sends stop condition to complete the LDOconfiguration.

Current Sense Mode (Monitoring the LDO Current)

As discussed above, in some embodiments of the invention, the SensorInterface provides a Current Sense Mode, which can be activated via I2Cusing the corresponding control register, e.g., with an address 0x08.When activated, the LDO current is sensed and a proportional voltage ispresent at the output of The Sensor Interface (ILDO=VOUT/RL). TheCurrent Sense Mode stays active until the Sensor Interface receives aninput select command from the microcontroller.

Further, in some embodiments, the current sense mode can be used tomonitor the change of the bridge impedance over time.

Sleep Mode (Analog Power Down)

In some embodiments of the Sensor Interface according to the invention,the Sleep Mode can be activated via I2C using the corresponding controlregister (e.g., with an address 0x05). When activated, The SensorInterface will enter Sleep Mode. During Sleep Mode, the analog portionof The Sensor Interface is disabled. It should be noted that allregister settings are retained during Sleep Mode.

In some embodiments, to save power, during the Sleep Mode, the nominalsupply current will drop below a predefined current, e.g., below 70 μAwith LDO on and below 45 μA with LDO off.

In some embodiments, the microcontroller/master I2C can read duringsleep mode the value in any control register that stores a configurationvalue. During Sleep Mode, the only I2C command from the microcontrollerthat can be received or processed is a wake up command or the LDO on/offcommand. All other register addresses will be ignored. The wake upcommand is used to return to normal operation (exiting Sleep Mode) andcan be written to a designated control register (e.g., 0x04).

It should become apparent from the discussion above that the sensorinterface according to the present invention integrates many separatebut required functions together on one chip for multiple sensorchannels. As such, the present invention improves the sensor sensitivityand accuracy by providing more conditioning and calibration functionswhile reducing noises due to interconnect between different conditioningfunction blocks as well as the footprint on precious board real estate.

Although the description above refers to input signals from bridgesensors, the sensor interface according to the present invention can beused with many different types of sensors for different applications,such as pressure and temperature sensors, strain gauge amplifier,industrial process controls, and weigh scales.

Although the present invention has been particularly described withreference to the preferred embodiments thereof, it should be readilyapparent to those of ordinary skill in the art that changes andmodifications in the form and details may be made without departing fromthe spirit and scope of the invention. It is intended that the appendedclaims encompass such changes and modifications.

What is claimed:
 1. A sensor interface comprising: an input selectorthat selects one or more sensor signals from a plurality of sensorsignals based on input selection control signal; an offset generatorthat generates an offset signal based on an offset control signal; and aprogrammable signal adjuster that adjusts at least one of the selectedsensor signals based on the generated offset signal and a signaladjustment control signal.
 2. The sensor interface of claim 1, whereinthe input selector comprises a multiplexer that receives the pluralityof sensor signals on the input side, the multiplexer being configured toselect one sensor signal based on the selection control signal.
 3. Thesensor interface of claim 2, wherein the multiplexer comprises adifferential multiplexer.
 4. The sensor interface of claim 1, furthercomprising a plurality of offset registers configured for storing offsetvalues, each offset register corresponding to a respective sensorsignal.
 5. The sensor interface of claim 1, wherein the offset generatoris configured to generate offset values with both polarity.
 6. Thesensor interface of claim 1, wherein the programmable signal adjuster isconfigured to provide a number of selectable gains for use in amplifyingsensor signals.
 7. The sensor interface of claim 1, further comprising acontrol interface unit that generates the input selection controlsignal, the offset control signal, and the signal adjustment controlsignal.
 8. The sensor interface of claim 7, wherein the controlinterface unit interfaces with an external circuit that receives and/orhandles output of the sensor interface.
 9. The sensor interface of claim7, wherein the control interface unit comprises a slave I2C serialdigital interface.
 10. The sensor interface of claim 7, wherein thecontrol interface unit generates a mode control signal configured forcontrolling or adjusting one or more characteristics of input signals tothe programmable signal adjuster.
 11. The sensor interface of claim 10,wherein the mode control signal causes a voltage present at both of anoutput of the input selector and an input of the programmable signaladjuster to be proportional to a current applied in at least one othercircuit in the sensor interface.
 12. The sensor interface of claim 1,further comprising a regulator that regulates power supply to aplurality of sensors generating the plurality of sensor signals.
 13. Thesensor interface of claim 12, further comprising a multiplexer thatselects between an output of the input selector and a signal from theregulator, and provides based on the selection an output to theprogrammable signal adjuster.
 14. The sensor interface of claim 1,further comprising an analog to digital converter (ADC) for convertingan analog output signal of the programmable signal adjuster to a digitaloutput.
 15. The sensor interface of claim 1, further comprising acomparator that compares an output of the programmable signal adjusterwith a reference signal, and provides an output that is configured foruse in performing offset correction to the selected sensor signal. 16.The sensor interface of claim 15, wherein the comparator causes acounter corresponding to the selected sensor signal to count up or countdown when the output of the programmable signal adjuster output does notmatch the reference signal.
 17. The sensor interface of claim 15,wherein the comparator causes a counter corresponding to the selectedsensor signal to stop counting and store the value of the counter intoan offset register for the selected sensor signal when the output of theprogrammable signal adjuster output matches the reference signal.